Seat for vehicle

ABSTRACT

Provided is a vehicle seat in which the transmission direction of deformation of a seat when an impact load is applied thereto is diffused so that impact absorbability is improved. This vehicle seat includes a seat back having a seat back frame that serves as a framework. The seat back frame has side frames positioned on the left and right sides, and a lower frame connecting lower parts of the side frames. The lower frame has a weakened part that is deformed when an impact load is applied, and a deformation guiding part for guiding the deformation direction of the weakened part. The weakened part and the deformation guiding part are arranged in the centers of areas obtained by extending the center portion of the lower frame toward the right and left sides with the same vertical-direction width, are provided on the same horizontal plane.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 14/443,233, filed May 15, 2015, which is the U.S. NationalStage Entry application of PCT Application No. PCT/JP2013/081048, filedNov. 18, 2013, which claims the priority benefit of Japanese PatentApplication No. 2012-253641, filed Nov. 19, 2012, the contents beingincorporated herein by reference.

BACKGROUND

Disclosed herein is a vehicle seat, and particularly, a vehicle seatwith improved impact energy absorption efficiency upon a rear-endcollision or the like.

Generally, when a so-called rear-end collision occurs, for example, whena vehicle is rear-ended or upon a significant collision occurring when avehicle travels rearward, a seated occupant suddenly moves rearward dueto an inertial force, and the occupant's upper body inclines rearward.

Various techniques have been proposed that are characterized by such aconfiguration that a side frame composing a seat back frame is bent whenthe sudden rearward movement of the occupant causes a rear load to beapplied to the seat back frame so that the impact load applied to theoccupant upon the rearward movement is mitigated (for example,International Patent Application Publication No. WO 2012/077764 (“the'764 Document”)).

A seat back frame of a vehicle seat disclosed in the '764 Documentincludes side frames positioned on right and left sides, and a lowerframe that connects lower parts of these side frames.

This lower frame is formed in a shape that is widened in a verticaldirection as it extends from a center portion thereof toward right andleft end portions thereof, and flexible narrow portions are formed inupper parts of the right and left end portions.

These narrow portions horizontally extend from both ends on the outersides in the right-left direction of the right and left end portionstoward the inner side of the seat, incline upward as they come towardthe inner side of the seat, and are formed in long shapes extendedtoward the upper edges of the right and left end portions.

The configuration is such that, when an impact load is applied to theseat, for example, upon a rear-end collision of the vehicle or the like,these narrow portions are deformed preferentially, and the deformationis transmitted from the narrow portions toward upper edges of the rightand left end portions.

In this way, by limiting deformed portions of the seat back frame,propagation of impact energy throughout the entirety of the seat backframe can be prevented, and impact energy can be absorbed stably.

In the vehicle seat as disclosed in the '764 Document, however,deformation is transmitted in one direction from the narrow portionstoward the upper edges of the right and left end portions when an impactload is applied, and it is impossible to diffuse the direction in whichwarping deformation is transmitted. Therefore, a vehicle seat has beendesired wherein impact absorbability is further improved, by diffusingthe transmission direction of warping deformation of the seat.

Besides, the vehicle seat as disclosed in the '764 Document includesnarrow portions that are preferentially subjected to warping deformationwhen an impact load is applied. Therefore, a vehicle seat in which therigidity of the seat back frame in normal use is further improved hasbeen desired.

Further, the narrow portions of the vehicle seat disclosed in the '764Document are included in the right and left end portions of the lowerframe, and are extend in long shapes from both ends on outer sides inthe right-left direction toward the inner sides in the right-leftdirection. Therefore, a vehicle seat has been desired that is capable ofsufficiently absorbing impact even when lengths of the narrow portionsin the extension direction are decreased in the case where areas wherethe narrow portions are formed are limited.

SUMMARY

Various embodiments of the invention were made in light of theabove-described problems, and it is an object of these to provide avehicle seat that is capable of diffusing the direction in which warpingdeformation of a seat is transmitted when an impact load is applied upona collision, particularly upon a rear-end collision, so that impactabsorbability is further improved.

It is another object to provide a vehicle seat that is warped anddeformed when an impact load is applied thereto to absorb the impactload, wherein rigidity of a seat back frame thereof in normal use isfurther improved.

It is still another object to provide a vehicle seat that includesweakened portions that sufficiently absorb impact when an impact load isapplied and that are formed in compact sizes.

The above-described problem is solved by embodiments of a vehicle seatthat include a seat back frame, wherein the seat back frame includesside frames that are positioned on right and left sides, and a lowerframe that connects lower parts of the side frames, wherein the lowerframe includes a weakened portion that is deformed when an impact loadis applied, and a deformation guiding portion that guides a direction ofthe deformation of the weakened portion, wherein the lower frame isformed so that a width in a vertical direction of a center portionthereof is smaller than a width in the vertical direction of right andleft end portions thereof, wherein the weakened portion is provided inan area obtained by extending the center portion of the lower frametoward right and left sides with the same vertical-direction width, andwherein the deformation guiding portion is provided at a positioncorresponding to the weakened portion as viewed in in the verticaldirection.

In this way, the weakened portion is provided in an area obtained byextending the center portion of the lower frame toward right and leftsides with the same vertical-direction width. Therefore, when an impactload is applied to the vehicle seat upon a rear-end collision or thelike, the transmission directions of upward and downward warpingdeformation of the weakened portion starting from the weakened portionas a starting point can be diffused more easily. Therefore, a vehicleseat with further improved impact absorbability can be provided.

Further, since the deformation guiding portion is provided at a positioncorresponding to the weakened portion as viewed in the verticaldirection, when an impact load is applied, the transmission direction ofdeformation starting from the weakened portion as a starting point isguided by the deformation guiding portion, whereby the deformationtransmission direction can be more easily diffused from the weakenedportion upward and downward.

Still further, since the weakened portion is provided in an areaobtained by extending the center portion of the lower frame toward rightand left sides with the same vertical-direction width in the lowerframe, the weakened portion can be formed in a compact size.

Here, the configuration may be such that upper and lower edges of thecenter portion extend horizontally, and upper and lower edges of theright and left end portions extend continuously from the upper and loweredges of the center portion to spread upward and downward, respectively,and either one of the upper and lower edges of the lower frame startsextending upward or downward at positions in closer proximity to theweakened portion, as compared with the other one.

In this way, since the upper and lower edges of the right and left endportions extend continuously from the upper and lower edges of thecenter portion to spread upward and downward, respectively, the rigidityof the seat back frame in normal use can be further improved.

Further, since either one of the upper and lower edges of the lowerframe starts extending upward or downward at positions in closerproximity to the weakened portion as compared with the other one, therigidity of the seat back frame can be ensured on the other side, whileon the one side, when an impact load is applied, deformation can beeasily allowed to occur preferentially in the transmission direction ofdeformation starting from the weakened portion as a starting point.Therefore, the seat back frame can be formed in such a shape that a partwith ensured rigidity and a part with a direction in which deformationis transmitted preferentially are taken into consideration.

Here, the configuration may be such that the weakened portion extendshorizontally in a right-left direction, and the weakened portion and thedeformation guiding portion are provided on a same horizontal plane.

In this way, the weakened portion and the deformation guiding portionare thus provided on the same horizontal plane. Therefore, thetransmission direction of deformation starting from the weakened portionas a starting point can be more easily guided by the deformation guidingportion, and the direction can be more easily diffused from the weakenedportion upward and downward.

Here, the configuration may be such that the vehicle seat furtherincludes a seat cushion frame that includes cushion side framespositioned on right and left sides, wherein at least a part of theweakened portion is positioned at a lower position than an upper end ofthe cushion side frame, and is arranged along an outer edge of thecushion side frame.

In this way, at least a part of the weakened portion is positioned at alower position than an upper end of the cushion side frame, and isarranged along an outer edge of the cushion side frame. Therefore, theweakened portion is arranged in close proximity to a portion connectedto the cushion side frame in the lower frame, and therefore, more easilyis subjected to concentration of stress due to an impact load.Therefore, the impact load can be absorbed efficiently. Further, theweakened portion is arranged along an outer edge of the cushion sideframe. Therefore, when the weakened portion is formed, interference withthe cushion side frame does not occur, and the operability is improved.

Here, the configuration may be such that the vehicle seat furtherincludes a reclining mechanism that rotatably connects the seat backframe with respect to the seat cushion frame, wherein: the recliningmechanism includes spring members that are mounted on the cushion sideframes and energize the seat back frame in an erected state; engagementmembers on which extension ends of the spring members are engaged arefixed on the lower frame; and the weakened portion is provided at alower position than portions where the engagement members are fixed.

In this way, the engagement members on which extension ends of thespring members are engaged are fixed on the lower frame and the weakenedportion is provided at a lower position than portions where theengagement members are fixed. Therefore, this weakened portion isarranged in close proximity to the reclining mechanism, particularly ina portion thereof that includes the spring member, in the lower frame.The weakened portion, therefore, is more easily subjected toconcentration of stress due to an impact load. As a result, an impactload is can be absorbed more efficiently.

Here, the configuration may be such that the right and left end portionsinclude deformation areas that are deformed due to an impact load fromthe weakened portion toward at least one of the upper and lower edges ofthe right and left end portions; the lower frame has at least one holeportion; and the hole portion is provided in the deformation areas.

In this way, the hole portion is provided in the deformation areas thatare deformed due to an impact load, in the right and left end portionsof the lower frame. Therefore, when an impact load is applied, thetransmission direction of deformation starting from the weakened portionas a starting point is easily diffused toward the hole portion. In otherwords, providing a hole portion in the lower frame makes it possible toguide the direction in which deformation is desirably transmitted fromthe weakened portion as a starting point.

Here, the configuration may be such that, in the upper and lower edgesof the right and left end portions, notch portions that are notched inthe deformation areas are formed; and the hole portions are provided onstraight lines extended between right and left inner-side ends of theweakened portions and the notch portions.

This configuration makes it possible that when an impact load isapplied, the transmission direction of deformation starting from theweakened portion as a starting point is easily diffused toward portionswhere the hole portions and the notch portions are formed.

Here, the configuration may be such that flange portions are provided onthe upper and lower edges of the lower frame, the flange portionsprotruding in a front to back direction from the upper and lower edges;and the flange portions are notched in the deformation areas, in theupper and lower edges.

In this way, the flange portions are provided in the upper and loweredges of the lower frame, and the flange portions are notched in thedeformation areas in the upper and lower edges. Therefore, when animpact load is applied, a transmission direction of deformation startingfrom the weakened portion as a starting point is easily diffused towardportions where the flange portions are notched in the upper and loweredges of the lower frame. In other words, providing portions where theflange portions are notched in the upper and lower edges of the lowerframe makes it possible to guide the direction in which deformation isdesirably transmitted from the weakened portion as a starting point.

Here, the configuration may be such that the deformation guidingportions are provided in the right and left end portions, in the lowerframe; the lower frame includes a protrusion portion in the centerportion; and the protrusion portion extends in the right-left directionbetween a pair of the deformation guiding portions.

In this way, the lower frame includes the protrusion portion in thecenter portion; and the protrusion portion extends in the right-leftdirection between a pair of the deformation guiding portions. Therefore,the provision of the protrusion portion ensures the rigidity of thelower frame, and stress concentration is easily achieved at the weakenedportions.

Therefore, the rigidity of the seat back frame in normal use can beimproved, and when an impact load is applied, stress concentration canbe achieved at the weakened portions, whereby the impact load can beabsorbed efficiently.

Here, the configuration may be such that the deformation guidingportions are provided in the right and left end portions, in the lowerframe; the weakened portions are provided on outer sides in theright-left direction, with respect to the deformation guiding portions;the lower frame includes a protrusion portion in the center portion; andthe protrusion portion extends, in the right-left direction, topositions interposed between the deformation guiding portions and theweakened portions.

In this way, the weakened portions are provided on outer sides in theright-left direction, with respect to the deformation guiding portions,and the protrusion portion extends, in the right-left direction, topositions interposed between the deformation guiding portions and theweakened portions. Therefore, the provision of the protrusion portionfurther ensures the rigidity of the lower frame, and stressconcentration is easily achieved at the weakened portions.

Here, the configuration may be such that the weakened portions areprovided in centers in areas obtained by extending the center portiontoward the right and left sides with the same vertical-direction width,in the lower frame.

This configuration makes it further easier to diffuse the transmissiondirections of warping deformation starting from the weakened portions asstarting points upward and downward with respect to the weakenedportions. Therefore, impact absorbability can be further improved.

Further, the weakened portions can be formed in compact sizes.

Here, the configuration may be such that the weakened portions areprovided in the right and left end portions, in the lower frame; andeach weakened portion includes a horizontal portion and at least one ofinclined portions, wherein the horizontal portion extends horizontallyin the right-left direction, and the inclined portions are an upwardinclined portion and a downward inclined portion that extendcontinuously from the horizontal portion to an inner side in theright-left direction to be inclined upward and downward, respectively.

This configuration makes it possible to easily diffuse the transmissiondirections of deformation starting from the weakened portions asstarting points toward a direction in which the at least one of theupward inclined portion and the downward inclined portion extends.

Since the weakened portions are provided in areas obtained by extendingthe center portion of the lower frame toward right and left sides withthe same vertical-direction width, when an impact load is applied upon arear-end collision or the like, the transmission directions of upwardand downward warping deformation of the weakened portions starting fromthe weakened portions as starting points can be diffused more easily.Therefore, a vehicle seat with further improved impact absorbability canbe provided.

Further, since the deformation guiding portion is provided at a positioncorresponding to the weakened portion as viewed in the verticaldirection, when an impact load is applied, the transmission direction ofdeformation starting from the weakened portion as a starting point isguided by the deformation guiding portion, whereby the deformationtransmission direction can be more easily diffused from the weakenedportion upward and downward.

Still further, since the weakened portion is provided in an areaobtained by extending the center portion of the lower frame toward rightand left sides with the same vertical-direction width in the lowerframe, the weakened portion can be formed in a compact size.

According to one or more embodiments, the upper and lower edges of theright and left end portions extend continuously from the upper and loweredges of the center portion to spread upward and downward, respectively,the rigidity of the seat back frame in normal use can be furtherimproved.

Further, since either one of the upper and lower edges of the lowerframe starts extending upward or downward at positions in closerproximity to the weakened portion as compared with the other one, therigidity of the seat back frame can be ensured on the other side, whileon the one side, when an impact load is applied, deformation can beeasily allowed to occur preferentially in the transmission direction ofdeformation starting from the weakened portion as a starting point.Therefore, the seat back frame can be formed in such a shape that a partwith ensured rigidity and a part with a direction in which deformationis transmitted preferentially are taken into consideration.

According to one or more embodiments, the weakened portion and thedeformation guiding portion are thus provided on the same horizontalplane. Therefore, the transmission direction of deformation startingfrom the weakened portion as a starting point can be more easily guidedby the deformation guiding portion, and the direction can be more easilydiffused from the weakened portion upward and downward.

According to one or more embodiments, at least a part of the weakenedportion is positioned at a lower position than an upper end of thecushion side frame, and is arranged along an outer edge of the cushionside frame. Therefore, the weakened portion is arranged in closeproximity to a portion connected to the cushion side frame in the lowerframe, and therefore, more easily is subjected to a concentration ofstress due to an impact load. Therefore, the impact load can be absorbedefficiently. Further, the weakened portion is arranged along an outeredge of the cushion side frame. Therefore, when the weakened portion isformed, interference with the cushion side frame does not occur, and theoperability is improved.

According to one or more embodiments, the engagement members on whichextension ends of the spring members are engaged are fixed on the lowerframe and the weakened portion is provided at a lower position thanportions where the engagement members are fixed. Therefore, thisweakened portion is arranged in close proximity to the recliningmechanism, particularly in a portion thereof that includes the springmember, in the lower frame. The weakened portion, therefore, is moreeasily subjected to concentration of stress due to an impact load. As aresult, an impact load is can be absorbed more efficiently.

According to one or more embodiments, the hole portion is provided inthe deformation areas that are deformed due to an impact load, in theright and left end portions of the lower frame. Therefore, when animpact load is applied, the transmission direction of deformationstarting from the weakened portion as a starting point is easilydiffused toward the hole portion. In other words, providing a holeportion in the lower frame makes it possible to guide the direction inwhich deformation is desirably transmitted from the weakened portion asa starting point.

According to one or more embodiments, when an impact load is applied,the transmission direction of deformation starting from the weakenedportion as a starting point can be easily diffused toward portions wherethe hole portions and the notch portions are formed.

According to one or more embodiments, the flange portions are providedin the upper and lower edges of the lower frame, and the flange portionsare notched in the deformation areas in the upper and lower edges.Therefore, when an impact load is applied, a transmission direction ofdeformation starting from the weakened portion as a starting point iseasily diffused toward portions where the flange portions are notched inthe upper and lower edges of the lower frame. In other words, providingportions where the flange portions are notched in the upper and loweredges of the lower frame makes it possible to guide the direction inwhich deformation is desirably transmitted from the weakened portion asa starting point.

According to one or more embodiments, the lower frame includes aprotrusion portion in the center portion; and the protrusion portionextends in the right-left direction between a pair of the deformationguiding portions. Therefore, the provision of the protrusion portionensures the rigidity of the lower frame, and stress concentration iseasily achieved at the weakened portions.

Therefore, the rigidity of the seat back frame in normal use can beimproved, and when an impact load is applied, stress concentration canbe achieved at the weakened portions, whereby the impact load can beabsorbed efficiently.

According to one or more embodiments, the weakened portions are providedon outer sides in the right-left direction, with respect to thedeformation guiding portions and the protrusion portion extends, in theright-left direction, to positions interposed between the deformationguiding portions and the weakened portions. Therefore, the provision ofthe protrusion portion further ensures the rigidity of the lower frame,and stress concentration is easily achieved at the weakened portions.

According to one or more embodiments, the transmission directions ofwarping deformation starting from the weakened portions as startingpoints can be more easily diffused upward and downward with respect tothe weakened portions. Therefore, impact absorbability can be furtherimproved. Further, the weakened portions can be formed in compact sizes.

According to one or more embodiments, the transmission directions ofdeformation starting from the weakened portions as starting points canbe easily diffused toward a direction in which the at least one of theupward inclined portion and the downward inclined portion extends.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a vehicle seat according to anembodiment.

FIG. 2 is a schematic perspective view of a seat frame according to anembodiment.

FIG. 3 is a rear view of a lower frame of the seat frame according to anembodiment.

FIG. 4 is an enlarged rear view of a lower frame according to anembodiment.

FIG. 5 is an enlarged right side view of a seat frame according to anembodiment.

FIG. 6 is an enlarged rear view of a lower frame that illustrates asecond embodiment of the present invention.

FIG. 7 is an enlarged rear view of a lower frame that illustrates athird embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The members, the arrangements, and the likedescribed below do not limit the invention, and may be modified intovarious forms in accordance with the spirit of the invention.

The present embodiment relates to an invention of a vehicle seat inwhich weakened portions and deformation guiding portions are provided inright and left end portions of a lower frame of a seat back frame, andthe weakened portions and the deformation guiding portions arepositioned in the centers in areas obtained by extending the lower framecenter portion toward the right and left sides with the samevertical-direction width.

A vehicle seat S of the present embodiment, as illustrated in FIG. 1,mainly includes a seat cushion 1, a seat back 2 located on a side of atop surface of the seat cushion 1, and a headrest 3 located on a side ofa top surface of the seat back 2, and further includes a seat frame Sathat functions as a framework illustrated in FIG. 2.

The side where an occupant is seated with respect to the seat back 2 ofthe vehicle seat S is the front side.

The seat cushion 1 is a seat portion that supports the occupant frombelow. A cushion pad 1 a is mounted on a cushion frame 10 functioning asa framework illustrated in FIG. 2, and an outer layer 1 b covers thecushion pad 1 a, whereby the seat cushion 1 is formed.

The seat back 2 is a backrest that supports the back of the occupantfrom behind. A cushion pad 2 a is mounted on a seat back frame 20functioning as a framework illustrated in FIG. 2, and an outer layer 2 bcovers the cushion pad 2 a, whereby the seat back 2 is formed.

The headrest 3 is a head portion that supports the head of the occupantfrom behind. A cushion pad 3 a is mounted on pillars (not illustrated)as a core, and an outer layer 3 b covers the cushion pad 3 a, wherebythe headrest 3 is formed.

The cushion frame 10 is formed with an approximately rectangular framebody that functions as a framework of the seat cushion 1. As illustratedin FIG. 2, the cushion frame 10 includes cushion side frames 11 providedon right and left sides; a pan frame 12 as a plate-like frame providedbetween front-side top surfaces of the cushion side frames 11; a frameconnecting pipe 13 as a connecting member provided between thevicinities of rear-side ends of the cushion side frames 11; and elasticsprings 14 that connect approximately central parts in the front to backdirection of the cushion side frames 11.

Each cushion side frame 11 is formed with a sheet metal member thatextends in the front to back direction. The cushion side frame 11 on theleft side and the cushion side frame 11 on the right side are separatedfrom each other in the right-left direction, in a state of beingparallel to each other.

Between the cushion side frames 11 and the seat back frame 20, asillustrated in FIG. 2, there is provided a reclining mechanism 15 thatrotatably connects the seat back 2 with respect to the seat cushion 1.

The reclining mechanism 15 has a known mechanism, and includes aconnecting shaft 16 that functions as a rotation axis for the recliningmechanism 15; coil springs 17 that energize the seat back frame 20 in anerected state; and spring engagement members 18 on which extension endsof the coil springs 17 are engaged.

The connecting shaft 16 is formed with a pipe member having anapproximately circular cross section that connects right and left endportions of the cushion side frames 11 and the seat back frame 20.

The connecting shaft 16 is connected, passing through shaftthrough-holes (not illustrated) provided at lower ends of right and leftend portions of the seat back frame 20, and shaft insertion holes (notillustrated) provided at rear ends of right and left end portions of thecushion side frames 11.

Each of the coil springs 17 is formed with a line member in a coilshape. The coil springs 17 are provided at rear ends of the right andleft outer side surfaces of the cushion side frames 11.

Ends on one side of the coil springs 17 are engaged and stopped on thespring engagement members 18, thereby being fixed at the lower ends onthe outer sides in the right-left direction of the seat back frame 20.Ends on the other side of the coil springs 17 are engaged and stopped onspring engagement portions (not illustrated) provided on right and leftouter side surfaces of the cushion side frame 11.

Each of the spring engagement members 18 is an approximately L-shapedmember obtained by bending a sheet metal member. An upper end of thespring engagement member 18 is fixed on the seat back frame 20. Thespring engagement member 18 includes a bent portion 18 a on a lower endthereof, the bent portions being bent toward outer sides in theright-left direction. One ends of the coil springs 17 are engaged andstopped on the bent portions 18 a.

An operation lever (not illustrated) is attached on an outer side of thecushion side frame 11. By operating this operation lever, the connectingshaft 16 is rotated so that the seat back 2 is rotated with respect tothe seat cushion 1.

The seat back frame 20 is an approximately rectangular frame body asillustrated in FIG. 2. The seat back frame 20 includes, on an upperside, an upper frame 21 that is formed with a hollow cylinder and isformed in an approximately reverse U shape; right and left side frames22 that are provided on the right and left sides to connect the upperframe 21; elastic springs 23 provided between approximately centralparts of inner side surfaces of the side frames 22; and a lower frame 30provided between lower end portions of the inner side surfaces of theside frames 22.

The side frames 22 and the lower frame 30 may be integrally formed.

Each of the right and left side frames 22 is obtained by bending edgesof a sheet metal member toward the inner side in the right-leftdirection, to have an approximately angular U-shape. The right and leftside frames 22 are extended in the vertical direction, and are separatedfrom each other in the right-left direction, in a state of beingparallel to each other.

Each of the right and left side frames 22 is formed in a shape graduallystretching out to the front side continuously as it comes from the upperside to the lower side, and includes a front bent portion 22 a bent froma front edge toward the inner side in the right-left direction, and arear bent portion 22 b bent from a rear edge toward the inner side inthe right-left direction.

On right and left inner side surfaces of the right and left side frames22, recessed portions 22 c that are recessed toward the inner sides inthe right-left direction, respectively. In the recessed portions 22 c,through holes that pass therethrough in the vertical direction areformed.

Right and left end portions of the elastic springs 23 are inserted intothe through holes of the recessed portions 22 c to be engaged andstopped, thereby being connected with the right and left side frames 22.

The lower frame 30 is obtained by bending edges of a sheet metal membertoward the front side, to have an approximately angular U-shaped crosssection. The lower frame 30 is composed of, as illustrated in FIG. 2, aframe main body portion 31 that extends in the right-left direction, andframe bent portions 32 formed by bending right and left ends.

Each of the frame bent portions 32 is arranged to be in contact with aninner side surface of the side frame 22, and an upper end of the framebent portion 32 and a lower end of the side frame 22 are welded andfixed to each other.

In the frame bent portions 32, shaft through-holes (not illustrated)that pass therethrough in the right-left direction are provided so thatthe connecting shaft 16 is fit through the shaft through-holes to beconnected to the frame bent portions 32.

On outer side surfaces of the frame bent portions 32, spring engagementmembers 18 are fixed with fastening bolts 38.

The frame main body portion 31 includes an upper edge flange portion 33a and a lower edge flange portion 33 b that protrude to the front side,as illustrated in FIG. 2.

The upper edge flange portion 33 a and the lower edge flange portion 33b are provided on an upper edge portion and a lower edge portion of theframe main body portion 31, respectively, and extend in the right-leftdirection.

As illustrated in FIG. 3, the frame main body portion 31 is composed ofan approximately rectangular frame center portion 34 that extends in theright-left direction, and right and left frame end portions 35 that areprovided on the right and left outer sides of the frame center portion34 and is widened as extending to have a greater width in the verticaldirection than the width of the frame center portion 34.

The frame center portion 34 includes a bead-shaped protrusion portion 36that protrudes to the front side in the lower edge part, and a pair ofrecessed portions 37 that are recessed downward in a top surfacethereof.

The protrusion portion 36 is formed to extend in the right-leftdirection, between the deformation guiding portions 50 provided on theright and left sides, thereby enhancing the rigidity of the lower edgepart of the lower frame 30.

The upper and lower edges of the frame center portion 34 extend towardthe right and left outer sides to be approximately horizontal. The upperand lower edges of the right and left frame end portions 35 extendtoward the right and left outer sides to be continuous from the upperand lower edges of the frame center portion 34, respectively, whilebeing inclined and spread upward and downward.

Here, the right and left frame end portions 35 are formed in such amanner that positions at which the upper edges start inclining upward ison the inner sides in the right-left direction with respect to positionsat which the lower edges start inclining downward, as illustrated inFIG. 3.

In other words, the upper and lower edges of the right and left frameend portions 35 are composed of upward-inclined edges anddownward-inclined edges, respectively, and inner-side ends of theupward-inclined upper edges are formed on inner sides in the right-leftdirection with respect to inner-side ends of the downward-inclined loweredges.

In the upper and lower edges of the right and left frame end portions35, there are provided a notch portion 39 a and a notch portion 39 b,which are notched toward weakened portions 40 that are described below.

In this way, in the upper and lower edges of the right and left frameend portions 35, parts thereof that include the notch portion 39 a andthe notch portion 39 b are formed as parts having low rigidity.

As illustrated in FIG. 4, each of the right and left frame end portions35 includes a weakened portion 40 having flexibility for deformationwhen an impact load is applied upon a rear-end collision or the like; adeformation guiding portion 50 that guides the transmission direction ofdeformation starting from the weakened portion 40 as a starting point;and an approximately circular hole portion 51.

The weakened portion 40 is a recessed portion that is recessed towardthe front side, and extends horizontally in the right-left direction.The weakened portion 40 is formed to have an arc-shaped vertical crosssection or a semi-circular arc-shaped vertical cross section.

The weakened portion 40 of the present embodiment is formed as arecessed portion that is recessed toward the front side, but theconfiguration is not limited to this. The configuration can be variedappropriately. For example, the weakened portions 40 may be formed to bethrough-holes that pass through the lower frame 30 in the front to backdirection.

The weakened portions 40 are arranged, in the right and left frame endportions 35, approximately at the width-direction centers in areasobtained by extending the frame center portion 34 toward the right andleft sides with the same vertical-direction width, and regarding theright-left direction, the weakened portions 40 are arranged at ends onthe right and left side frame sides, as illustrated in FIG. 4.

The positions where the weakened portions 40 are arranged are notlimited to the centers as described above, as long as the weakenedportions 40 are arranged within the areas obtained by extending theframe center portion 34 toward the right and left sides with the samevertical-direction width.

As illustrated in FIG. 5, the lower end 40 b of each weakened portion 40is arranged, as viewed in the vertical direction, at a lower positionthan a top surface of a connecting shaft fixing portion 11 a that isprovided behind the cushion side frame 11, and is formed in closeproximity to a circular arc outer edge 11 b of the connecting shaftfixing portion 11 a, to be along the circular arc outer edge 11 b.

Further, the weakened portions 40 are arranged, as viewed in thevertical direction, in close proximity to parts at lower positions thanportions where the spring engagement members 18 are fixed with thefastening bolts 38, in the lower frame 30.

A portion where the weakened portion 40 is arranged is a portion that isapproximately in the center in the width in the vertical direction inthe frame center portion 34, at a lower position than a portion wherethe spring engagement member 18 is fixed, and above a portion where theconnecting shaft 16 is connected. Therefore, this portion has a highrigidity.

In normal use of the vehicle seat S, therefore, it is possible tomaintain the rigidity of the seat back frame 20 at a high level.

When an impact load is applied to the seat back frame 20 upon a rear-endcollision or the like, the weakened portion 40 is collapsed in thevertical direction, whereby the upper part of the lower frame 30 and theside frames 22 are bent rearward.

Here, the upper end 40 a and the lower end 40 b of the weakened portion40 illustrated in FIG. 5 control a collapse amount of the weakenedportion 40, that is, controls a rearward inclination angle of the sideframe 22 so that the rearward inclination angle should not exceed apredetermined value.

In other words, when the weakened portion 40 is significantly collapsedin the vertical direction, the upper end 40 a and the lower end 40 b ofthe weakened portion 40 come into contact with each other, whereby asituation in which the lower end 40 b presses and stops the upper end 40a is achieved.

Accordingly, by appropriately adjusting the width in the verticaldirection and the width in the front to back direction of the weakenedportion 40, the collapse amount of the weakened portion 40, that is, therearward inclination angle of the side frame 22, can be adjusted.

The deformation guiding portion 50 is a projected portion that projectsrearward as illustrated in FIG. 4. The deformation guiding portion 50extends horizontally in the right-left direction, and is formed to havea triangular-shaped vertical cross section. More specifically, thedeformation guiding portion 50 has surfaces that incline from an upperend and a lower end thereof toward the center, and is projected toward aside opposite to the side of the weakened portion 40.

In the right and left frame end portions 35, the deformation guidingportions 50 are arranged in close proximity to the weakened portions 40in such a manner that the deformation guiding portions 50 are providedon the same horizontal plane as the weakened portions 40, and arearranged on the right and left inner sides in the right-left direction,in other words, on the frame center portion 34 sides.

In this way, the deformation guiding portions 50 are projected on a sideopposite to the side of the weakened portions 40, and are arranged inclose proximity to the weakened portions 40 in such a manner that thedeformation guiding portions 50 are provided on the same horizontalplane as the weakened portions 40. Therefore, the rigidity of the lowerframe 30 can be enhanced.

The shape of the deformation guiding portion 50 is not limitedparticularly, and may be changed appropriately. The deformation guidingportion 50 is projected on a side opposite to the side of the weakenedportion 40, but may be projected to the same side as the weakenedportion 40. The deformation guiding portion 50 is arranged on the samehorizontal plane as the weakened portion 40, but may be arrangedslightly above or below in the vertical direction.

In the lower-end-side inclined surface of the deformation guidingportion 50, an approximately circular hole portion 50 a is formed.

The hole portion 50 a is formed as a hole for attachment of anothermember such as a harness or the like.

Next, the transmission direction of deformation occurring when an impactload is applied to the vehicle seat S upon a rear-end collision, whichstarts from the weakened portion 40 as a starting point, is describedwith reference to FIG. 4.

When an impact load is applied to the seat back frame 20, the weakenedportion 40 is deformed to be warped in the vertical direction, andfurther, the warping deformation is transmitted toward the right andleft inner sides in the lower frame 30, which causes the lower frame 30and the side frames 22 to be bent rearward.

Here, on the right and left inner sides of the right and left weakenedportions 40 in the lower frame 30, the deformation guiding portions 50that are projected toward the side opposite to the side of the weakenedportions 40 are provided on the same horizontal plane. Therefore, thetransmission direction of the warping deformation is diffused to beinclined upward and downward, avoiding the deformation guiding portions50, as indicated by the directions of arrows illustrated in FIG. 4.

The upward-inclined transmission directions of deformation starting fromthe weakened portions 40 as starting points are directed toward thenotch portions 39 a, which are provided at the upper edges of the rightand left frame end portions 35, and the downward-inclined transmissiondirections of deformation are directed toward the notch portions 39 b,which are provided at the lower edges of the right and left frame endportions 35.

In this way, when an impact load is applied to the vehicle seat S, thewarping deformation can be transmitted from each weakened portion in twodirections, i.e., the upward direction and the downward direction withrespect to each weakened portion as a starting point. Therefore, ascompared with the case where warping deformation is transmitted in onedirection, the impact absorbability can be enhanced further.

Besides, with the deformation guiding portions 50 thus provided, thetransmission direction of deformation starting from the weakened portion40 as a starting point can be guided in preliminarily set directions.

In the present embodiment, portions extended between the weakenedportions 40 and the notch portions 39 a provided at the upper edges ofthe right and left frame end portions 35, and portions extended betweenthe weakened portions 40 and the notch portions 39 b, serve asdeformation areas that are deformed due to an impact load.

The lower frame 30 of the present embodiment is formed in such a mannerthat positions at which the lower edges of the right and left frame endportions 35 start inclining downward are in closer proximity to theweakened portions 40, as compared with positions at which the upperedges start inclining upward, as illustrated in FIG. 4. In other words,the configuration is such that the rigidity of the lower edges of theright and left frame end portions 35 is smaller than the rigidity of theupper edges thereof.

The configuration is, therefore, such that when an impact load isapplied, the transmission direction of deformation starting from theweakened portion 40 as a starting point is guided preferentiallydownward.

By contrast, the configuration may be such that positions at which theupper edges of the right and left frame end portions 35 start incliningupward are in closer proximity to the weakened portions 40, as comparedwith positions at which the lower edges start inclining downward. Inthis case, the transmission directions of deformation starting from theweakened portions 40 as starting points are guided preferentiallyupward.

Further, the configuration is such that the hole portions 50 a areformed on the lower end side of the deformation guiding portions 50 sothat the rigidity is smaller below the deformation guiding portions 50.When an impact load is applied, therefore, the transmission directionsof deformation starting from the weakened portions 40 as starting pointstend to be guided further preferentially downward.

The hole portions 51 are formed as holes for attachment of anothermember such as a harness or the like, and are provided in a portionextended between the weakened portion 40 and the notch portion 39 a, andin a portion extended between the weakened portion 40 and the notchportion 39 b, respectively. In other words, the hole portions 51 areprovided in areas that are between the weakened portions 40 and thedeformation guiding portions 50 as viewed in the right-left directionand between the weakened portions 40 and the notch portions 39 a, 39 bas viewed in the vertical direction.

In this way, the hole portion 51 are provided so that low-rigidityportions are provided in the deformation areas as second weakenedportions. When an impact load is applied, therefore, the transmissiondirections of deformation starting from the weakened portions 40 asstarting points tend to be guided further preferentially toward thenotch portions 39 a, 39 b.

The hole portions 51 may be formed as recessed portions or thinportions, other than the through holes.

Next, a lower frame 60 according to a second embodiment of the presentinvention is described with reference to FIG. 6.

The lower frame 60 includes a bead-shaped protrusion portion 61 thatprotrudes to the front side in the lower edge part, and weakenedportions 62 formed as recessed portions that are recessed toward thefront side.

The protrusion portion 61 extends in the right-left direction in such amanner that right and left ends thereof are positioned between thedeformation guiding portions 50 and the weakened portions 62, wherebythe rigidity of the lower edge part of the lower frame 60 is enhanced.

The weakened portion 62 is formed to have an arc-shaped vertical crosssection or a semi-circular arc-shaped vertical cross section, andextends in the right-left direction.

The weakened portion 62 is composed of a horizontal portion 62 a thathorizontally extends, as well as an upward inclined portion 62 b thatextends to incline upward, and a downward inclined portion 62 c thatextends to incline downward, which extend continuously from thehorizontal portion 62 a to the inner side in the right-left direction.

The upward inclined portion 62 b and the downward inclined portion 62 cextend toward the notch portion 39 a and the notch portion 39 b providedat the upper and the lower edges of the lower frame 60, respectively.

Thus, the weakened portion 62 includes the upward inclined portion 62 band the downward inclined portion 62 c. When an impact load is appliedto the vehicle seat S, therefore, the transmission direction of warpingdeformation starting from the weakened portion 62 as a starting pointcan be easily diffused to two directions toward the notch portion 39 aand the notch portion 39 b, respectively.

Next, a lower frame 70 according to a third embodiment of the presentinvention is described with reference to FIG. 7.

The lower frame 70 includes slits 71 provided in the notch portions 39 bin the lower edge part, and weakened portions 72 formed as recessedportions that are recessed toward the front side.

The slit 71 is formed in an approximately V-shaped notch that is notchedtoward the weakened portion 72, and a part that includes the slit 71 haslower rigidity.

The weakened portion 72 is formed to have an arc-shaped vertical crosssection or a semi-circular arc-shaped vertical cross section, andextends in the right-left direction.

The weakened portion 72 is composed of a horizontal portion 72 a thathorizontally extends, and a downward inclined portion 72 c that extendsto incline downward continuously from the horizontal portion 72 a to theinner side in the right-left direction.

The downward inclined portion 72 c extends toward the notch portion 39 bprovided at the lower edge of the lower frame 60.

When an impact load is applied to the vehicle seat S, the transmissiondirection of warping deformation starting from the weakened portion 72as a starting point is diffused to two directions toward the notchportion 39 a and the notch portion 39 b.

Here, as the weakened portion 72 includes the downward inclined portion72 c, the transmission direction of warping deformation starting fromthe weakened portion 72 as a starting point can be guided preferentiallytoward the notch portion 39 b side.

Further, as the lower frame 70 includes the slit 71, the transmissiondirection of warping deformation starting from the weakened portion 72as a starting point can be guided further preferentially toward thenotch portion 39 b side.

In each of the above-described embodiments, a front seat of anautomobile is described as a specific example, but the present inventionis not limited to this. It is needless to say that the present inventionis applicable to a middle seat and a rear seat of an automobile.

REFERENCE NUMERALS S vehicle seat Sa seat frame 1 seat cushion 1a, 2a,3a cushion pad 1b, 2b, 3b outer layer 2 seat back 3 headrest 10 cushionframe 11 cushion side frame 11a connecting shaft fixing portion 11bouter edge 12 pan frame 13 frame connecting pipe 14 elastic spring 15reclining mechanism 16 connecting shaft 17 coil spring 18 springengagement member 18a bent portion 20 seat back frame 21 upper frame 22side frame 22a front bent portion 22b rear bent portion 22c recessedportion 23 elastic spring 30, 60, 70 lower frame 31 frame main bodyportion 32 frame bent portion 33a upper edge flange portion 33b loweredge flange portion 34 frame center portion 35 right and left frame endportions 36, 61 protrusion portion 37 recessed portion 38 fastening bolt39a, 39b notch portion 40 weakened portion 40a upper end 40b lower end50 deformation guiding portion 50a, 51 hole portion 62, 72 weakenedportion 62a, 72a horizontal portion 62b upward inclined portion 62c, 72cdownward inclined portion 71 slit

What is claimed is:
 1. A vehicle seat comprising: a seat back frame,comprising: side frames that are positioned on right and left sides, anda lower frame that connects lower parts of the side frames; wherein: thelower frame comprises: a plurality of weakened portions that aredeformed when an impact load is applied, and a plurality of deformationguiding portions that guide directions of the deformation of theplurality of weakened portions; the plurality of weakened portions areprovided at a position corresponding to the plurality of deformationguiding portions as viewed in a vertical direction of the seat backframe; the plurality of deformation guiding portions are provided inright and left end portions of the lower frame; the lower framecomprises a protrusion portion in a center portion of the lower frame;and the protrusion portion extends in a right-left direction of the seatback frame between a pair of the plurality of deformation guidingportions.
 2. The vehicle seat according to claim 1, wherein: theprotrusion portion is disposed at a lower position than the plurality ofweakened portions.
 3. The vehicle seat according to claim 1, wherein:the protrusion portion is disposed at a lower position than theplurality of deformation guiding portions.
 4. The vehicle seat accordingto claim 1, wherein: the protrusion portion is disposed in a lower halfpart of the lower frame.
 5. The vehicle seat according to claim 1,wherein: the plurality of weakened portions and the plurality ofdeformation guiding portions are positioned in a same horizontal plane,and the protrusion portion is disposed below the same horizontal plane.6. The vehicle seat according to claim 1, wherein: the plurality ofweakened portions are disposed on an outer side of the plurality ofdeformation guiding portions in the right-left direction; and theplurality of deformation guiding portions are disposed on an outer sideof the protrusion portion in the right-left direction.
 7. The vehicleseat according to claim 1, wherein: the plurality of weakened portions,the plurality of deformation guiding portions and the protrusion portionare arranged spaced apart from each other in the right-left direction.